Recent digital copying machines implement advanced functions by processing images as digital information. As functions other than those of a copying machine, such copying machine can also have a printer function by establishing connection to a network, a FAX function by establishing connection to a public line, and the like. For example, digital copying machines GP55F, GP215, and the like available from Canon inc. are known.
FIG. 1 shows an example of the arrangement of a digital copying machine, which is connected to a host computer (to be abbreviated as a “PC” hereinafter) via a network. Referring to FIG. 1, reference numeral 101 denotes a PC; and 103, a digital copying machine. The PC 101 and digital copying machine 103 are connected via a network cable 102. In the digital copying machine 103, reference numeral 104 denotes an image processor, which includes an image memory (page memory) 105.
The user launches so-called DTP (Desk Top Publishing) application software on the PC 101 and creates or edits various documents or figures. The created document or figure is converted into a page description language (PDL, e.g., PostScript available from Adobe Systems Incorporated), and is sent as image data to the copying machine 103 after it is rasterized. At this time, the image data is sent as RGB luminance data, and the copying machine 103 that has received the image data sometimes executes luminance-density conversion, an image conversion process, or the like in some cases. However, image data normally undergoes a luminance-density conversion process, image conversion process, or the like implemented by a software process of a driver on the PC 101, and is then sent.
Of course, when the PC 101 sends PDL data, since the PDL data must be rasterized to bitmap data, an external controller (not shown) is connected between the PC 101 and copying machine 103 to execute the aforementioned process.
However, the prior art suffers the following problem.
Normally, when the image conversion process is executed in the driver on the PC 101, since processes of an average density preservation method, error diffusion method, and the like impose heavy loads, much time is required to process the entire image, and the user must wait until a desired output is obtained.